Use of radiation-induced polymers in cement slurries

ABSTRACT

Water loss from cement slurries is reduced by incorporating within a cement slurry a polymer obtained as a product of radiation-induced polymerization of acrylamide and/or methacrylamide and acrylic acid, methacrylic acid, and/or alkali metal salts thereof. The polymerization is preferably carried out in 10-60% aqueous monomer solution with gamma radiation. The aqueous monomer solution preferably contains 25-99% acrylamide and 75-1% sodium acrylate. The polymer can be present in concentration of about 0.001 to about 3.0 weight percent, based on the aqueous phase of the slurry.

Knight et al.

[ 1 USE OF RADIATION-INDUCED POLYMERS IN CEMENT SLURRIES [75] Inventors:Bruce L. Knight; John S. Rhudy;

William B. Gogarty, all of Littleton, C010.

[73] Assignee: ICI United States Inc., Wilmington,

Del.

[22] Filed: Nov. 6, 1972 [21] Appl. No.: 303,736

[52] U.S. C1. 166/295; 166/247; 166/294 [51] Int. Cl E21b 33/13 [58]Field of Search 166/247, 275, 294, 295

[56] References Cited UNITED STATES PATENTS 3,114,419 12/1963 Perry eta1. 166/295 3,152,641 10/1964 Boyd 166/295 3,336,979 8/1967 Ingraham eta1 166/294 3,490,533 l/1970 McLaughlin 166/295 3,493,529 2/1970Krottingcr et a1. 166/295 3,502,149 3/1970 Pence 166/295 1 Apr. 15, 19753,749,172 7/1973 Hessert et a1. 166/295 FOREIGN PATENTS OR APPLICATIONS683,476 3/1964 Canada 166/275 Primary ExaminerStephen J. NovosadAssistant ExaminerJack E. Ebel Attorney, Agent, or Firm.1oseph C.Herring; Richard C. Willson, Jr.; Jack L. Hummel [57] ABSTRACT Waterloss from cement slurries is reduced by incorporat'ing within a cementslurry a polymer obtained as a product of radiation-inducedpolymerization of acrylamide and/or methacrylamide and acrylic acid,methacrylic acid, and/or alkali metal salts thereof. The polymerizationis preferably carried out in 10-60% aqueous monomer solution with gammaradiation. The aqueous monomer solution preferably contains 25-99%acrylamide and 75-1% sodium acrylate. The polymer can be present inconcentration of about 0.001 to about 3.0 weight percent, based on theaqueous phase of the slurry.

16 Claims, No Drawings USE OF RADIATION-INDUCED POLYMERS IN CEMENTSLURRIES CROSS REFERENCE TO RELATED APPLICATIONS The following patentapplications relate to the general field of this invention:

Scr. No. 303.735. filed Nov. 6. I972;

Ser. No. 303.737. filed Nov. 6. I972;

Ser. No. 303.743. filed Nov. 6. I972:

Ser. No. 307.713. filed Nov. 17. 1972.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to improving the water loss properties of cement slurries duringthe cementing of oil wells. such is accomplished by incorporating withinthe cement slurry a polymer obtained by radiation inducedpolymerization.

2. Description of the Prior Art Additives have been admixed with cementslurries to reduce the water loss from the cement slurry into thesubterranean formation during cementing thereof. By preventing waterloss. better cementing jobs can be obtained. Extensive water loss canresult in formation damage resulting from cement filtrate waters andflash setting. the latter resulting in a cement having undesirably lowstrength.

Agents such as carboxymethylcellulose and hydroxyethyl cellulose. clayssuch as bentonite. and like additives have been added to reduce waterloss. It is especially important to prevent water loss when cementing aporous formation from which the mud cake has been removed. i.e.. thecement may become quickly dehydrated and undergo a so-called flash set."Such an adversity may cause the pipe to stick and prevent the rotationor reciprocation desirable when wall scratches are used in the hole.Wall scratches" are used to improve the bond between the cement and theformation. the scratchers actually scratching the interior of thewell-bore so that the cement can more readily bond to the formationwall.

Good fluid loss control properties of the cement slurry are essential.especially to control the deposition of solids wherein a differentialpressure exists between the cement slurry and the permeable zones of theformation to be cemented. Also. during the cementing of easing. if theformation has highly permeable zones, this may cause prematuredehydration of the cement slurry and thus a less effective cementingjob. Also. in squeeze cementing. controlled deposition facilitatesfilling all of the perforations without excessive squeeze pressures-ifhigh fluid loss is realized, then of course controlled deposition willnot be effected.

Other reasons exist for using radiation-induced polymers in cementslurries; for example, the slurries are easier to pump into the wellboreif they experience low water loss characteristics. and as a result. lessenergy is required to pump the cement slurry down into the wellbore.Also. lower pump pressures, in turn. can reduce water loss problems.Also. the slurry viscosity tends to maintain better stability if thewater loss characteristics are reduced. thus enabling one to design thecementing job more effectively and efficiently.

The prior art has tried high molecular weight syn-- thetic polymers asfluid loss control agents for cement slurries. Examples of such polymersinclude commercially available. partially hydrolyzed polyacrylamides.

SUMMARY OF THE INVENTION Reduction in fluid loss from cement slurries aswell as reduction of friction loss during the pumping of the cementslurry into the well bore is accomplished by incorporating within theaqueous phase of the cement slurry a water-soluble polymer obtained byradiation polymerization of acrylamide and/or methacrylamide and acrylicacid. methacrylic acid and/or alkali metal salts thereof. The aqueoussolution to be polymerized contains 10-60% by weight of monomer; themonomer preferably is 25-995 acrylamide and -1 sodium acrylate. byweight. Radiation intensity is preferably 250-1 .000.000 rads/hr and theradiation dosage is preferably 500 to about 300,000 rads. The reactionproduct may be diluted with water and used directly. or the polymer maybe extracted from the reaction product. dried and thereaftersolubilized. Concentrations of about 0.001 to about 3.0 weight percent,all based on the aqueous phase of the slurry. are useful.

PREFERRED EMBODIMENTS OF THE INVENTION The monomer is a combination ofat least one compound selected from the group consisting of acrylamideand methacrylamide and at least one compound selected from the groupconsisting of acrylic acid. methacrylic acid alkali metal acrylate. andalkali metal methacrylate. Small amounts of additional cthylenicallyunsaturated copolymerizable monomers may also be used. Preferably. themonomer is a mixture of acrylamide and sodium acrylate. It is preferredthat the monomer contain about l75% and preferably 15-55% and morepreferably 20-50% of acrylic acid or alkali metal salt thereof. e.g..sodium acrylate.

Irradiation of the monomer is preferably carried out in aqueous solutioncontaining about 10% to about 60% and more preferably about 15% to about45% by weight of dissolved monomer. At the lower concentrations ofmonomer the product is generally a pourable polymer solution. Atconcentrations of above about l5% by weight the product is generally anonpourable gel. A water-insoluble product may result at concentrationsabove about 60% monomer; thus. such high concentrations are undesirable.Of course. the particular limits of monomer concentration will depend.among other things. on the radiation conditions used. monomers used. andon the desired product for a particular use. The intrinsic viscosity ofthe polymer product increases as the monomer concentration increases. upto the point where the amount of cross-linking becomes appreciable.provided all other variables are held constant.

The aqueous monomer solution preferably should not contain more thanabout 5 ppm of transition metal ions. such as nickel. iron. and cobalt.and no more than about 0.5 ppm of cuprous and cupric ions.

Irradiation of the aqueous monomer solution may be accomplished withhigh energy ionizing radiation. The radiation used has a wavelengthbelow 3,500 Angstroms and preferably below 2.000 Angstroms. Theradiation employed may be particulate or electromagnetic in nature.Examples include accelerated electrons. protons. neutrons. etc.. as wellas X-rays and gamma-rays. the latter being preferred.

Radiation intensity is preferably about 1,000 to about 300,000 rads/hr.and more preferably about 5,000 to about 200,000 rads/hr. Intensitydirectly influences the molecular weight of the polymer. That is. underotherwise identical conditions, low intensities generally give highermolecular weight polymers.

The radiation dose is preferably at least about 1,000 rads and morepreferably at least about 1,500 rads. The maximum dose level ispreferably not more than 100,000 rads and more preferably not more than50,000 rads.

The radiation dose used directly influences the intrinsic viscosity anddegree of monomer-to-polymer conversion. At a given radiation intensityand monomer concentration, an increase in radiation dose generally tendsto result in a decrease in the intrinsic viscosity of the polymerproduced. The radiation dose may also influence the water-solubility ofthe polymer, as it has been found that too high a radiation dose mayrender the resulting polymer water-insoluble. At the preferred dosagerates, conversion up to about 100% and preferably 80-l00% of the monomerto polymer may be obtained without undue insolubilization.

The pH of the aqueous monomer solution is generally not critical exceptthat very low pH values may cause insoluble products to form. Preferablythe pH is within the range of 3-13 and more preferably about 8 to aboutl l. Although higher and lower pH values may be used, it should berecognized that hydrolysis tends to occur at pH values much below about3 and more above about l l. While the process described above may beused to prepare polymers having an intrinsic viscosity from about 6 toabout dl/g (deciliters per gram) in 2 normal sodium chloride at 25.5C,the process is modified somewhat to prepare polymers having an intrinsicviscosity below about 6 dl/g or above about 30 dl/g in 2 normal sodiumchloride at 255C. Polymers having an intrinsic viscosity below about 6dl/g are prepared by carrying out the polymerization reaction describedabove in the presence of a chain transfer agent. The chain transferagent tends to restrict the growth of the active polymer chains, therebyresulting in the formation of polymers having lower molecular weightsand lower intrinsic viscosities. The chain transfer agents which may beused herein may be any chain transfer agent which tends to restrict thegrowth of the polymer chains and thereby aid the formation of lowermolecular weight and lower intrinsic viscosity polymers and which issoluble in the reaction medium. Illustrative examples of chain transferagents which may be used include lower alkyl alcohols, such as methanol,ethanol, and isopropanol; halogenated compounds, such as trichloraccticacid; thiosorbitols containing two thio groups and four secondaryhydroxyl groups; and mercaptans. The concentration of chain transferagent used depends upon the intrinsic viscosity desired, the monomerconcentration, and the chain transfer constant of the chain transferagent used. The use of a chain transfer agent is not necessary in orderto prepare polymers having intrinsic viscosities from about 6 to about30 dl/g; but if desired, such polymers may be prepared in the presenceof a chain transfer agent.

In order to prepare polymers having intrinsic viscosities above about 30dl/g, the polymerization reaction is terminated when less than about 75%and preferably when less than about 60% by weight of the monomer hasbeen converted to polymer. It has been found that the intrinsicviscosity of the resulting polymer tends to decrease as the percentconversion of monomer to polymer increases. For reasons of economy, itis not practical to tolerate conversions lower than about 20%.

The variables of radiation intensity, total radiation dose, and monomerconcentration discussed above are interdependent variables. While usefulpolymers may be prepared at all monomer concentrations, radiationintensities, and radiation dosages within the ranges given heretofore,all combinations of concentration, dose, and intensity within theseranges may not be used to prepare polymers useful in the process of thisinvention. For example, while a polymer useful in the process of thisinvention may be prepared at a monomer concentration of 60% by weight,provided the radiation dose used is sufficiently low to result in theformation of water-soluble polymers, the use of a monomer concentrationof 60% by weight, an intensity of 250 rads per hour, and a dose of300,000 rads, results in the formation of water-insoluble polymers. inview of this interdependency of intensity, dose, and monomerconcentration, it may be necessary to perform a limited amount ofexperimentation in order to prepare a polymer having the desiredintrinsic viscosity. However, this experimentation may be kept to aminimum in view of the disclosure in Table 1 below of the preparation ofa variety of polymers of different viscosities and in view of thediscussion above on the effect of intensity, dose. monomerconcentration, degree of conversion, and chain transfer agent on theintrinsic viscosity of the polymer. Accordingly, the reaction conditionswhich may be used to prepare a water-soluble polymer having an intrinsicviscosity different from the intrinsic viscosities of the polymersdescribed in Table I may be readily determined by minor modification ofthe reaction conditions given in Table l for the preparation of thepolymer having the intrinsic viscosity nearest to the intrinsicviscosity of the polymer which is desired to be prepared. Suchmodification may be made in view of the above discussions on the effectof intensity, dose, monomer concentration, percent conversion of monomerto polymer, and chain transfer agent on the intrinsic viscosity of thepolymer. For example, a polymer having an intrinsic viscosity of about16 dl/g may be prepared by using the same reaction conditions employedin Example F in Table 1, except that the radiation intensity isincreased, the total radiation dose is increased, the monomerconcentration is lowered, the

percent monomer conversion is increased, and/or the.

reaction is carried out in the presence ofa chain transfer agent. it isgenerally preferred, however, that the said decrease in intrinsicviscosity be obtained by increasing the radiation intensity, loweringthe monomer concentration, and/or using a chain transfer agent.

The product of irradiation is an aqueous solution of water-solublepolymer which may be in the form of a pourable liquid or a nonpourable,rubbery gel, depending upon the polymer concentration and the intrinsicviscosity of the polymer. The viscosity of the polymer solution tends toincrease as the polymer concentration and intrinsic viscosity of thepolymer increase. Polymer solutions produced by the radiation may beadmixed with water and used directly or the polymer solution may beconcentrated by conventional means or it may be recovered in particulateform, ie. dry form. For example, a nonpourable gel may be finelysubdivided and the water removed by conventional drying techniques. Or.the water may be extracted from the subdivided gel with awater-miscible. volatile organic liquid which has no affinity for thecopolymer. e.g.. with methanol.

The polymer may contain cations which are preferaoly monovalent cationsand more preferably sodium.

The polymers obtained from this radiation polymerization generally haverelatively low Huggins constants. This constant is related to thelinearity of the polymer where molecular weights are constant. i.e.. fortwo copolymers having similar molecular weights but different Hugginsconstant. the lower Huggins constant indicates a more linear polymer.Polymers having Huggins constants below I and preferably below 0.7 andmore preferably below 0.5 are most often used with this invention. Incertain applications. a mixture of polymers having low, medium. and/orhigh Huggings constants may be desired to obtain improved oil recovery.A more detailed definition of Huggins constant and a method fordetermining the Huggins constant ofa polymer is found in Textbook ofPolymer Chemistry. Billmeycr. lnterscience Publishers. N.Y.. 1957. pp.128439.

Intrinsic viscosity of the polymer can vary from less than about 1 toabout 60 deciliters per gram and preferably is about 5 to about 35deciliters per gram. The permeability of the reservoir rock willinfluence the desired intrinsic viscosity. Generally speaking. lowintrinsic viscosities can be used with lower permeabilities. Forexample. permeabilities less tha about 50 md will permit the use ofintrinsic viscosities less than about It). whereas permeabilities ofabout 200 md or more will generally demand intrinsic viscosities greaterthan and up to about -30. The intrinsic viscosity numbers referred toare measure in a 2 normal sodium chloride solution at 255C. Of course.polymers having very high intrinsic viseosities are desired in verypermeable reservoirs. It can generally be concluded that theeffectiveness of the polymer increases as the intrinsic viscosityincreases. Mixtures of polymers having different intrinsic viscositiesmay also be used.

The polymer may be solubilized in water before the cement is admixed.Water containing large amounts of polyvalent metallic cations ispreferably avoided since such ions can adversely influence the viscosityand water-solubility of the polymer. The concentration of polyvalentmetallic cations which may be present in the aqueous polymer solution isdependent upon the specific polyvalent metallic cation present. thetemperature and pH of the solution. and the intrinsic viscosity andanionic content of the polymer. in general, the polymer becomes lesstolerant of polyvalent metallic cations as the intrinsic viscosity.anionic content. and concentration of the polymer increase. The use ofwater containing substantial amounts of copper ions and/or iron ions ispreferably avoided due to the adverse effect such ions may have on thepolymer. such water-solubility of the polymer. etc.

Shearing of the polymer upon dissolution and injection into the wellbore should be avoided if maximum effectiveness as a water loss agent isdesired. To obtain maximum polymer properties with the gel form of thepolymer. the gel is first extruded and then cut into fine pieces. e.g..the size of BBs. and thereafter agitated in agueous solution at lowshear rates. Pumps character-- ized by low shear rates as well asagitators run at low shear rates are especially useful. Water-solublealkaline salts. that is. salts which give pH above 7 in water. such asalkali metal carbonates. may be added to the agueous solution tofacilitate solubilization of the polymer. A preferred alkaline salt issodium carbonate.

It may be desired that the copolymer, upon contact with the reservoirrock. be adsorbed or absorbed onto the reservoir rock. Where such isdesired, the copolymer preferably has a very low anionic content. e.g.,from above about 0 up to about 30% and preferably less than 15% ofcarboxylic groups onto the copolymer chain. That is. the copolymercontains less than 30% and preferably less than 15% sodium acrylate.Also. preferably. the polymer has at least some branching onto the mainpolymer chain. For a given molecular weight polymer. this means that thepolymer has a relatively high Huggins constant which constant indicatesbranching of the polymer.

Where it is desired that the polymer have some reduced degree of watersolubility. for example. about 20% water solubility at about 100F. thepolymer can be partially cross-linked. Cross-linking can be effected byoverradiating. i.e., by continuing the radiation after all monomer hasbeen converted to polymer. or by continuing the radiation after thewater solubility of the polymer begins to decrease. Polyfunctionalmonomers such as ethylenically unsaturated water-soluble.copolymerizable monomers containing more than one ethylenicallyunsaturated double bond. may be used to reduce the water solubility ofthe polymer. The polyfunctional monomers may be used in concentrationsof about 0.01 to about 10%. preferably about 0.05 to about 5% and morepreferably about 0.l to about 3% by weight. The copolymerizablepolyvalent monomers are added to the aqueous solution beforeirradiation. Examples of such monomers include methylene bisacrylamide.polyacrylates such as sorbitol polyacrylates and polyallyl ethers ofsorbitol. e.g.. hexallylsorbitol.

Where it is desired to have polymers having the highest intrinsicviscosities. the radiation polymerization should take place at lowradiation intensities. low eonversions. and high monomer concentrations.Of course. the above relative values are within the previously indicatedreaction conditions set out herein.

To produce polymers having high intrinsic viscosities, e.g.. about 30 toabout 60, and low Huggins constants. the radiation intensity ispreferably 5.000 to about 50.000 rads/hr and the monomer concentrationis preferably about 20 to about 60% and preferably 25 to 50% and theconversion is preferably about 15 to about and more preferably less thanabout 50%.

The polymer is preferably present in concentrations of about 0.001 toabout 3.0 weight percent. more preferably about 0.002 to about 2.0weight percent and more preferably about 0.005 to about 1.0 weightpercent within the water phase of the cement slurry. Of course. otheradditives besides the polymer. water. and cement may be present in thecement slurry. but it is preferred that the additives not react with thepolymer to sufficiently override the beneficial influence of the polymerto the cement slurry. These additives are known in the art as well asthe different methods of eementing wells. including cementing the casingwithin the well bore as well as cementing thief" zones. creatingimpermeable barriers within a horizontal strata within a well bore influid communication with the formation.

Cement slurries useful with this process generally contain less thanabout 30% to about607: or more water. Cementing of injection wells.production well (both oil and water), disposal wells. thieving zonesduring drilling operations. *squeeze" cementing of formations or zones.and like operations are applicable with this invention.

The polymers of this invention can be selected to exhibit highviscositics at low shear ratesthis property facilitates suspension ofparticles and agents within the cement slurry. etc. Also. the polymerexhibits low viscosities at high shear rates.

Also. the polymer can be selected to have improved shear degradationcharacteristics. That is. polymers generally tend to degrade as theypass through a region of high shear rate. e.g.. the cement slurry passesthrough valves. pipe fittings. etc. By selecting a polymer with somedegree of branching or some degree of cross-linking. the polymer will beless sensitive to shear degradation.

After the formation has been contacted with the cement slurry of thisinvention. drilled through and optionally acidized. it may be desirableto treat the formation with an aqueous hydrazine or hypochloritesolution. or a strong mineral acid to restore the permeability of theformation that has been contacted with the polymer. That is. thehydrazine. hypochlorite. or acid tends to chemically degrade the polymerand thus tends to restore at least some of the permeability to thereservoir rock that has been contacted with the polymer.

The following examples are presented to teach specific workingembodiments of the invention; such are tion contains 75% by weightacrylamide (AAd) and 2571 by weight sodium acrylate (NaAA) and has atotal monomer concentration of 21.4% by weight. The solution is purgedwith N; for 20 minutes and thereafter sealed. The sample is irradiatedwith cobalt 60 gamma radiation at an intensity of 18.000 rads/hr (R/hr)to a total dose of 8.800 rads (R). The resulting product is a gel-likemass.

A portion of the gel is weighed. and thereafter extracted with methanolto precipitate the polymer. The polymer is dried in a vacuum oven at 36Cand 0.02 psia for 24 hours and then to a constant weight at l 10C.Weight of the dried product divided by the theoretical weight gives amonomer conversion of 93%.

A portion ofthe gel is solubilized in water by first extruding itthrough a meat grinder; the spaghetti-like extrusion is cut into BB sizeparticles and then dissolved in water by agitating at a low rpm toprevent substantial shearing of the polymer.

The residue of the gel is recovered in dry powder form by firstextruding the gel, then dissolving it in water and thereafter addingmethanol to precipitate the polymer out of the solution. The polymer isthen ground to less than -mesh size and finally dried at 60C in a vacuumoven.

The intrinsic viscosity is measured at 255C in a 2 normal NaCl aqueoussolution. The Huggins constant is measured by the method described inTextbook of Polymer Chemistry, Billmeyer, Interscience Publishers. NewYork. 1957. pp. 128-139.

The monomer used in Sample G is dissolved in water.

containing 9.1% by weight of methanol.

TABLE 1 INFORMATION ON POLYMER SAMPLES Intrinsic Huggins Monomer TotalMonomer Viscosity Constants AAd/NaAA C oneen- Intensity Dose Additive Com'ersion Gel Powder Gel Powder Polymer Wt. Ratio tration ("/11 pH(R/hr.) (R) ("/11 ('71) (dl/g) (dl/g) F 70/30 24 9.5 100.000 15.000 8618.5 0.24 G 70/30 27 9.5 20.000 1 1.500 MeOH 9.1 91 12.4 11 7 0.31 0.38

H 70/30 13 9.5 220.000 44.000 MeOH 15 96.5 1.0

J 70/30 95 220.000 44.000 MeOH 15 84.0 6.9 0.52

not meant to limit the interpretation of the invention. EXAMPLE 1 Unlessotherwise specified. all percents are based on volume.

Preparation of the Copolymers To show that the copolymers of thisinvention impart unexpected results over polymers and copolymers of theprior art. this example is presented.

Fluid loss control properties are simulated in the laboratory byflooding water-saturated reservoir core samples with aqueous polymersolutions at a frontal velocity of 10 ft/day. The permeability reductionof the front section of the core is determined by first flooding thecore with water (containing 500 ppm total dissolved solids) at thevelocity of 10 ft/day and thereafter flooding the cores with the aqueouspolymer solutions indicated in Table 2. A high permeability reduction ofcores is desirable to minimize fluid loss from a cement slurry. Theaqueous polymer solutions are dissolved in TABLE 2 5. The process ofclaim 1 wherein one of the monomers is sodium methacrylate.

RESLLTS OF POLYMER FLOODING [N 100200 md SANDSTONF. CORES BrookfieldFlushed Perme- Permeability Viscosity lnitial Permeability abilityReduction it 6 rpm (md) (md) Run Polymer (Cp) 1 A 26.7 107 0.5 214 2 B32.2 142 1.5 93 3 C 27.2 I32 )9 150 4 D 20.0 110 0.6 I78 5 B 8.8 l59 I.3 I24 6 B 7. l 97 0.7 143 7 Partially hydrolyzed polyacrylamide 16.3135 2.5 54 8 (opolymer No. 1 39.0 123 2.6 47 9 Copolymer No. 2 33.5 1345 5 Runs 1-4 contains loo ppm poly mcr dissohcd in \\atcr containingabout 500 ppm TDS. Run 5 contains 300 ppm poly mcr dissohctl in outercontaining about 500 ppm 'l'DS. Run (1 contains 700 ppm polymertlissohcd in ater containing lX.000-20.000 ppm 'I'DS. Runs 7-9 containM00 ppm polymer dissohcd in utcr containing about 500 ppm 'I'DS. ('oolymcr No. 1 2 a commercially a ailahlev anionic acrylamitle copolymerobtained by a chemically catalyvcd polymerization reaction: has anintrinsic iscosity of 12.5 and a Huggins constant ol'0.34.

(o otymcr No. 2 z a commercially a ailable. \ery high molecular eightvstrongly anionic co olymer ol'acrylamide obtained y a chemicallycatalyzed polymcri/ation reaction; has an intrinsic \iscosity of 22.0and a Huggins constant ol'tLlR Partially hydroly/cd polyacrylantitlc acommercially auiilablc. partially hydrolyvcd. high molecular cightpolyaccrylaniidc obtained by a chemically y'ataly ycd poly merirationreaction: has an intrinsic \iscosity of 12.7 and a Huggins constantottLStv.

be incorporated within the scope of this invention as defined in thespecification and appended claims.

What is claimed is:

1.1n the process of cementing a well in fluid communication with asubterranean reservoir wherein a cement slurry is injected down the wellbore, the cement slurry containing a high molecular weight polymerdissolved in the water phase of the cement slurry to inhibit fluid lossfrom the cement slurry. the step comprising incorporating within theaqueous phase of the cement slurry a polymer obtained as a product ofhigh energy ionization radiation polymerization of at least one monomerselected from the group consisting of acrylamide and methacrylamide andat least one monomer selected from the group consisting of acrylic acid,methacrylic acid. alkali metal acrylate. and alkali metal methacrylatein concentrations of about 10% to about 60% by weight dissolved monomerin an aqueous medium. the radiation intensity being about 250 to about1,000,000 rads/hr and the radiation dose being about 500 rads to about300,000 rads.

2. The process of claim 1 wherein one of the monomers is acrylic acid.

3. The process of claim 1 wherein one of the monomers is methacrylicacid.

4. The process of claim 1 wherein one of the monomers is sodiumacrylate.

The above data indicate that Runs 16, as compared to Runs 7-9. exhibithigher permeability reductions than do the commercially availablepolymers and copolymers. Such large permeability reduction is a directindication of the fluid loss control properties of 21 ccment slurry whensuch polymers are used. Polymer E of Table l at the same concentrationand water conditions as copolymers No. l and No. 2. has a Brookfieldviscosity at 6 rpm of 52 cp.

It is not intended that this invention be limited by the above examples.Rather. compositions and components of cementing slurries known in theart and which are obvious to those skilled in the art are intended to 6.The process of claim 1 wherein one of the monomers is acrylamide.

7. The process of claim 1 wherein the polymer is a copolymer obtained bycopolymerizing acrylamide and sodium acrylate.

8. The process of claim 1 wherein the radiation intensity is within therange of about 1.000 to about 300,000 rads/hr.

9. The process of claim 1 wherein the radiation dose is within the rangeof about 1.000 to about 100.000 rads.

10. The process of claim 1 wherein the aqueous medium is at a pH withinthe range of about 3 to about 13.

11. The process of claim 1 wherein the pH of the aqueous medium iswithin the range of about 8 to about 1 1.

12. In the process of cementing a well in fluid communication with asubterranean reservoir wherein a cement slurry is injected down the wellbore. the cement slurry containing a high molecular weight polymerdissolved in the aqueous phase of the cement slurry to inhibit fluidloss from the slurry. the step comprising incorporation within the waterof the cement slurry a polymer obtained as a product of radiationcopolymerization of an aqueous solution comprised of about 10 to aboutof a mixture of about 25 to about 99% of acrylamide and about to about1% of sodium acrylate. the radiation intensity being within the range ofabout 250 to about 1.000.000 rads/hr. and the radiation dose being about500 rads to about 300.000 rads.

13. The process of claim 12 wherein the copolymer obtained from theradiation polymerization is in the form of a gel.

14. The process of claim 12 wherein the aqueous medium contains fromabout to about 45% of acrylamide and about 1571 to about 55% ofsodiumacrylate.

15. The process of claim 12 wherein the radiation is gamma radiation.

16. The process of claim 12 wherein the sodium acrylate is present in aconcentration of about 20% to about

1. IN THE PROCESS OF CEMENTING A WELL IN FLUID COMMUNICATION WITH ASUBTERRANEAN RESEVOIR WHEREIN A CEMENT SLURRY IS INJECTED DOWN THE WELLBORE, THE CEMENT SLURRY CONTAINING A HIGH MOLECULAR WEIGHT POLYMERDISSOLVED IN THE WATER PHASE OF THE CEMENT SLURRY TO INHIBIT FLUID LOSSFROM THE CEMENT SLURRY, THE STEP COMPRISING INCORPORATING WITHIN THEAQUEOUS PHASE OF THE CEMENT SLURRY A POLMER OBTAINED AS A PRODUCT OFHIGH ENERGY IONIZATION RADIATION POLYMERIZATION OF AT LEAST ONE MONOMERSELECTED FROM THE GROUP CONSISTING OF ACRYLAMIDE AND METHACRYLAMIDE ANDAT LEAST ONE MONOMER SELECTED FROM THE GROUP CONSISTING OF ACRYLIC ACID,METHACRYLIC ACID, ALKALI METAL ACRYLATE, AND ALKALI META METHACRYLATE INCONCENTRATIONS OF ABOUT 10% TO ABOUT 60% BY WEIGHT DISSOLVED MONOMER INAN AQUEOUS MEDIUM, THE RADIATION INTENSITY BEING ABOUT 250 TO ABOUT1,000,000 RADS/HR AND THE RADIATION DOSE BEING ABOUT 500 RADS TO ABOUT300,000 RADS.
 2. The process of claim 1 wherein one of the monomers isacrylic acid.
 3. The process of claim 1 wherein one of the monomers ismethacrylic acid.
 4. The process of claim 1 wherein one of the monomersis sodium acrylate.
 5. The process of claim 1 wherein one of themonomers is sodium methacrylate.
 6. The process of claim 1 wherein oneof the monomers is acrylamide.
 7. The process of claim 1 wherein thepolymer is a copolymer obtained by copolymerizing acrylamide and sodiumacrylate.
 8. The process of claim 1 wherein the radiation intensity iswithin the range of about 1,000 to about 300,000 rads/hr.
 9. The processof claim 1 wherein the radiation dose is within the range of about 1,000to about 100,000 rads.
 10. The process of claim 1 wherein the aqueousmedium is at a pH within the range of about 3 to about
 13. 11. Theprocess of claim 1 wherein the pH of the aqueous medium is within therange of about 8 to about
 11. 12. In the process of cementing a well influid communication with a subterranean reservoir wherein a cementslurry is injected down the well bore, the cement slurry containing ahigh molecular weight polymer dissolved in the aqueous phase of thecement slurry to inhibit fluid loss from the slurry, the step comprisingincorporation within the water of the cement slurry a polymer obtainedas a product of radiation copolymerization of an aqueous solutioncomprised of about 10 to about 60% of a mixture of about 25 to about 99%of acrylamide and about 75 to about 1% of sodium acrylate, the radiationintensity being within the range of about 250 to about 1,000,000rads/hr. and the radiation dose being about 500 rads to about 300,000rads.
 13. The process of claim 12 wherein the copolymer obtained fromthe radiation polymerization is in the form of a gel.
 14. The process ofclaim 12 wherein the aqueous medium contains from about 85% to about 45%of acrylamide and about 15% to about 55% of sodium acrylate.
 15. Theprocess of claim 12 wherein the radiation is gamma radiation.
 16. Theprocess of claim 12 wherein the sodium acrylate is present in aconcentration of about 20% to about 50%.